Phase modulation



Oct. 12, 1937. c. w. HANSELL 2,095,327

PHASE MODULATION Filed Dec. 12, 1954 3 Sheets-Sheet 1 29,161 )0 I? 1 1:: //a i 5 IC i c a c (ARR/ER l l I 1* 70 40 .50 60 20 30 may; M/JVAA/MA/ffil/J PHASE 05144770 'NVENTOR c. w. HANSELL Oct. 12, 1937. c. w. HANSELL 2,095,327

PHASE MODULATION Filed D80. 12, 1934 3 Sheets-Sheet 2 Oct. '12, 1937. c. w. HANSELL PHASE MODULATION 3 Sheebs-Sheet v13 Filed Dec. 12, 1934 kwkm @5333 km udwsmw INVENTOR c.w. HANSELL BY 7; W

ATTORNEY Patented Oct 12, 1937 ,r w s.

PHASE MODULATION Clarence W. Hansell, Rocky Point, N. Y., as-

signor to Radio Corporation of America, a corporation of Delaware Application December 12, 1934, Serial No. 757,140

3'7 Claims.

' 5 pearing in the output of a phase modulator to increase the purity of the transmitted wave. What I obtain is a phase modulated wave equivalent to an amplitude modulated wave except that the relative phase of carrier to side frequencies has been shifted 90. Thus, I obtain a final modulated wave of the same purity and band Width as an amplitude modulated wave whereas the usual phase modulated Wave contains higher order side frequencies and occupies a greater frequency band than an amplitude modulated wave. My form of phase modulated wave may be transformed into a perfect amplitude modulated Wave in a receiver by simply changing the phase .of the carrier Wave 90 with respect to the side frequencies; This can not be done with the usual phase modulated wave because the higher order side frequencies would cause harmonic distortions of the modulation after the carrier phase is shifted.

In eliminating or reducing undesired side frequencies dueto the modulation of the phase of a carrier wave in a transmitter, operated with a radio frequency output of constant power,I propose to eliminate the undesired frequenceis by introducing a supplemental modulation of the output wave in a direction and an amount such as to balance, or tend to balance, the undesired side frequencies.

In my United States Patent No. 1,849,620, issued March 15, 1932, I have shown a method of and means for reducing the radiation of undesired frequencies from the output of a transmitter by introducing a band-pass filter. The filter arrangement as shown and claimed in said patent is applicable to a transmitter using any kind of modulation but in general it eliminates only those undesired frequencies which lie outside the allowable transmission band. Other undesired frequencies within the transmission band are not affected by said filter. The present method and means reduces all undesired frequencies including those in the transmission band. The reduction of undesired frequencies is permissible in phase modulation signalling and does not in any manner] whatever reduce the linearity of the modulation or the efficiency of the signalling.

The novelfeatures of my invention have been pointed out in detail hereinafter as required by law.

My novel method of reducing or eliminating the undesired frequencies appearing in the output of a normal phase modulator, and circuit arrangements for accomplishing the same will be described in the following specification. In describing said method and means reference will be made to the attached drawings in which:

Figures 1a, 1b, 2 and 3 are vector diagrams and curves utilized in explaining my improved method of signalling; Figures 4 and 5 are circuit arrangements including the essential elements of the'present invention. These circuits may also include any other elements known in the art today which are necessary to signalling by means of phase modulation without departing from the spirit of the present invention; while Figures 6 and 7 illustrate additional means to be used with the circuits of Figures a and 5 to correct or reduce undesired frequencies in the output of a phase modulator. These means may be used alone or may supplement other means in said circuits for reducing distortion.

In order that the component frequencies in- Volved and the relations existing between the component frequencies in modulated waves may be clear I have drawn vector ing .saidwaves and their relation with respect to the carried wave etc. in Figures 1a and lb.

In Figure la, I have shown the very well known vector representation of three different points on the modulation of a carrier Wave by a single audio frequency assuming that the carrier wave has been amplitude modulated by said signal wave. a and b are vectors representing the side frequencies, 0 is the vector representing the carrier wave and d is the vector representing the resultant of the two side frequencies and the carmen In Figure lo I have shown the same vectors, (representing three different points on the mod ulation of a carrier wave) as in Figure id, but have changed the phase angle of the carrier with respect to the side bands by 90 degrees. This corresponds to changing from amplitude modulation to phase modulation. 7

In Figure 1a itwill be noted that the vector sum of the two side frequencies, a, b, always gives a resultant which adds to or subtracts from the carrier 0 directly, whereas in Figure It th vector sum of the two side frequencies is always at right angles to the carrierc as shown.

In Figure 1?) it will'be noted that as the side frequencies add to the carrier to swing or shift the phase thereof the vector sum of the carrier and the side frequencies does not remain condiagrams representstant but varies up and down in amplitude. The resultant d is increased above the value of the carrier when the phase is deviated in either direction. Thus amplitude modulation is accomplished to a certain extent in some phase modulators.

In phase modulators known heretofore in the art where it is desirable to remove amplitude modulation inadvertently accomplished in the phase modulated wave, the fluctuations in strength of the resultant wave are suppressed or removed by passing the phase modulated energy through an amplitude limiter of any type such as for example an overexcited thermionic tube. In fact the common definition of a pure phase modulated wave'is one whose phase is varied in proportion to the modulation voltage but whose amplitude or strength is constant. Consequently, as can be seen from Figure 1?), one cannot represent the ordinary pure phase modulated wave as a carrier and one pair of side frequencies per modulating frequency. Except at very low phase deviations, there must be other side frequency components added to the complex wave to hold its amplitude constant. The carrier and the two side frequencies alone cannot truly represent the ordinary pure phase modulated wave transmitted. The additional frequencies introduced constitute side frequencies corresponding to modulations by even numbered harmonics of the fundamental modulating frequencies. Also, if a number of modulating frequencies are present together, there must be introduced, in addition, frequencies which are not harmonics of the various modulating frequencies.

In Figure 2, I have shown a vector diagram indicating a number of phase positions of a constant amplitude or pure phase modulated wave at 15 degree intervals. The lines I have marked with Xs represent the vector sums of all of the unwanted side frequencies for each of the indicated angles of deviation. Thus as the carrier phase is to be deviated in either direction without change of amplitude i. e., pure phase modulation there must be forces acting in the modulation circuits to reduce the transmitter output by the amount represented by the vectors X, the direction of the forces being represented by arrow heads. If one could introduce other forces in the circuits of the transmitter to oppose the currents or forces represented by the X vectors one might 7 reduce or eliminate the undesired side frequencies and produce a phase modulated frequency spectrum of lesser width, which would be identical with the spectrum for amplitude modulation except for the phase of the carrier being shifted 90 degrees. This wave which I propose to produce may be called a quasi-phase modulated wave. This may be accomplished by means for causing the phase modulated energy output of the transmitter to increase by just the right amount as the phase of the carrier is deviated by any amount, in either direction, from its normal or zero value. In this manner I produce a phase modulated output of changing amplitude which may be represented by the straight line in Figure 3.

In Figure 3, I have plotted a curve of the values of the vectors X for various phase deviations of the carrier. If I increase the output of a transmitter by the percentage amounts indicated for various phase deviations of the carrier in either direction I can substantially eliminate undesired frequencies, thereby improving the quality of the phase modulation, the efiiciency thereof and preventing the wave of my signalling system from interfering with adjacent signalling waves.

Briefly, I accomplish the above objects by passing some of the transmitter modulation input energy through a full wave rectifier and using the rectified energy, without any smoothing to produce an upward modulation of the transmitter output, an amount dependent upon the amplitude of the modulating potentials and consequently proportional to the phase deviation of the carrier. This upward modulation varies approximately as the square of the phase deviation which is in turn proportional to the amplitude of the modulating potential. In general the elimination of the undesired side frequencies may be accomplished in a sufficient degree if I amplitude modulate the transmitter with the rectified energy a correct amount, while at the same time the unrectified signal energy is utilized to modulate the phase of the transmitter output. The output of the rectifier varies approximately as the square of the input.

In Figures 4 and 5 I have shown schematically two of the many ways of carrying out my method of reducing undesired frequencies in phase modulated energy. In these figures I have omitted all details not necessary to an understanding of the invention and have shown only enough elements to enable another radio engineer to put my scheme into practice. Of course, in practice I contemplate the use of all or most of the detail elements commonly used in transmitters of this type.

In Figure 4, a source of constant radio frequency energy 2, which may include a piezo-electric crystal or a low power factor electrical circuit is coupled to a phase modulator 4. The source 2 may include amplifiers and/or frequency multipliers to increase the amplitude and/or frequencies of the wave to the desired extent. The phase modulator 5 may be of any well known type such as has been disclosed by Crosby United States application No. 701,797 filed Dec. 11, 1933, Usselman United States application No. 616,026 filed June 8, 1932, Patent #2,035,165 dated March 31, 1936, Hansell United States application No. 640,370 filed Oct. 31, 1932, Patent #1,999,190 dated April 30, 1935, or Crosby United States application No. 690,330 filed Sept. 21, 1933. Moreover if desired I may combine source 2 and phase modulator a into a single stage since methods are available for directly phase modulating the output of oscillators. See Goldstine United States application No. 654,372 filed January 31, 1933, Patent #2961081, dated January 5, I937.

The phase modulator supplies phase modulated radio frequency energy to an amplifier system B. The amplifier system 8 may include one or more amplifier stages and may also include one or more frequency multiplier stages. In order to simplify the disclosure of this. present invention I have shown a single stage amplifier at 8. The amplifier system B may in turn energize an antenna, a line or any other transmission circuit. The control grids of the amplifier tubes in 8 are connected in pushpull relation with the phase modulator as shown. The anode electrodes of the tubes of the amplifier 8 may be connected in pushpull relation as shown by means of an inductance l2 which may be tuned to the mean frequency of the phase modulated energy by the variable condenser shown. The inter-electrode capacity of the tubes in 8 may be neutralized if desired by neutralizing capacities connected as shown or screen grid tubes may be used instead. The

anode electrodes of the tubes in 8 are supplied with potentials by way of a lead l4 connected as shown to a source It. The, anodes of the amplifiers 8 are also supplied with energy through a modulation choke MC, inserted in lead M, from a pair of modulator tubes at 20. The modulator tubes at it supply thedesired compensating amplitude modulation to the energy in the output of the tubes of stage 8 to reduce the undesired side frequencies in the output of said power amplifier. of modulation ofthe amplifier is used.

The modulating tubes in 26 have their screen grid electrodes connected to a full wave rectifier 22 which is in turn coupled by way of a transformer tothe source of modulating potentials 6. Any known form of rectifier may be used at 22, the one shown being merely for purposes of illustration. The modulating potentials from E are rectified in 22 and the pulsating output of the said rectifiers of double the modulating potential frequency, the intensity of which depends upon the amplitude of the signal potentials, is fed to the screen grid electrodes of the modulator tubes in 29. This pulsating modulating current is superimposed upon direct current from the source 24 connected as shown by way of a resistance R to the screen grid electrodes of the tubes in 28. The control grids of the tubes in 20 are supplied by the necessary biasing potentials from the source 26. The potential on the screen grids of the tubes in 2 is determined in part by the intensity of the current in B. This combination when arranged in accordance with my invention causes the anode current of the tubes in 25 to decrease more and more rapidly as the rectifier output increases. Since the modulation choke MC tends to hold the current flowing therein constant, a decrease in anode current to the screen grid tubes in Zll must be accompanied by an increase in anode current input to and alternating current output from the power amplifier 8. When all circuit elements such as resistances are of the proper size and potential adjustments are correct a very great reduction "in undesired frequencies in the output of the antenna or other utilization circuit may be obtained. Furthermore, by the use of proper elements in the circuit this reduction may be made such as to restrict the outputsidefrequencies to those which would be obtained with amplitude modulation so that a high degree of phase modulation (large phase swing) may be used without widening the overall frequency band.

If desired, I may modify the circuits of Fig. 4 by interchanging the connections to the sources a 2d and 26, interchanging theconnections to the ties or directions of the rectifiers in 22.

grids'of each tube in 26 and reversing the polari- In this case application'of either polarity of modulation will swing the potential of the control grids of the tubes in 2Q more negative. This will decrease the current to the anodes of the tubes in 20 and increase the input to the amplifier 8. Also, if desired, I may use three electrode tubes in 2D or I may use tubes with more than four electrodes.

The circuit arrangement of Figure 5 is similar in many respects to the arrangement in Figure 4. However, in Figure 5 the action of the rectifier 22 may be reversed as shown with respect to the action of the same rectifier in Figure l. In Figure 5 a transformer MT is used in place of the modulation choke MC. Due to the transformer action and the action of the rectifier and modu- In this arrangement the Heising method the sum of the potentials increases.

later tubes in 20 an increase in rectified modulation potential output causes an increase of the current in the anode of the modulating tubes in 20 and this acting through the transformer increases the input to the power amplifier. The modulating tubes in 2i! are operated at that point in their characteristics such that when no modulating currents are present in the transformer connectedwith the rectifier 22, the anodes of the tubes in 2i! draw little or no current. Then as the modulating potential input is increased the modulating tubes in 2% draw increasing values of anode current. The anode current inthese tubes increases about as the curve of Figure 3 indicates and the transformer steps up the voltage change due to current flow change and modulates up the energy in the output of the tubes of 8 due to phase modulation and thereby tends to balance out all of undesired frequencies from the output circuit of the amplifiers in 8.

In practice the simple circuits indicated in Figures 4 and 5 may be modified by the addition of fixed or automatically variable resistors in various parts of the rectifier and modulation circuits for more nearly approaching perfection in operating characteristics. These elements have not been shown in Figures 4 and 5 because their locations and values depend upon the characteristics and adjustments of individualtubes and equipment and so may vary greatly between different installations. As an example of automatically variable resistance I have'in mind the material manufactured by the General Electric Company, known as Thyrite. Oxide rectifiers, some types of photovoltaic cells, thermionic tubes etc. when used as resistors, also vary their resistance automatically when the potentials upon them or the currents through them are varied. Likewise curvatures in the characteristics of amplifiers may be used to advantage in many instances for obtaining overall characteristics which give the desired results.

In Figure 4, the resistor R, if made entirely or in part of 'I'hyrite, will tend to decrease the variations in screen grid potential of the tubes 29 and will considerably modify the response to V modulating potentials. If the resistor R is made of Thyrite, it will tend to make variations in screen grid potential more rapid and will increase thev curvature of the response to modulation potentials. Y

, In Figure 5, if we make the resistor R partly or wholly of Thyrite we will decrease the curvature in the response to modulating potentials, on the other hand, if We place the 'I'hyrite in resistor:

R we will accentuate the curvature of the response characteristic.

In Figure 4 the rectifiers in 22 may consist of Thyrite resistors. In the connections shown rectcurrent potential from the positive source shown and to an alternating current potential from the modulation source. Under these circumstances Thyrite has a rectifying action in that the alternating currentis partly converted a relatively heavy increase in current occursfiz.

which increases at a higher and higher rate as When the alternating current potential opposes the direct current potential the current decreases but less each Thyrite resistor would be subject to a 'di- ?6 and less rapidly as the difference of the .potenr tials approaches zero. The result is that Thyrite resistors with superimposed direct current and modulating potentials distort the modulating currents in the manner required for carrying out the object of my invention.

From Figure 2 it may be seen that the phase deviation required to produce side frequencies with a combined amplitude proportional to the modulation voltage, is not directly proportional to the modulation voltage. The angle of phase deviation required becomes relatively smaller at higher modulation voltages. Therefore, the phase modulator should have a curved or drooping response characteristic. Any radio engineer is familiar with a number of detail arrangements for distorting the modulation to produce this result. For exampla'the tubes used in the modulator 4 of Figs. 4 and 5 may have their potentials adjusted to obtain a non-linear response in phase deviation in response to modulating potentials. Also a non-linear amplifier may be used between the source 6 and the modulator 4. Another method is to connect non-linear resistance, such as Thyrite, across the leads from source 6 to modulator 4. This latter method is illustrated in Figures 6 and '7.

The distortion may be produced by utilizing the curvature in the characteristics of vacuum tubes or it may be obtained more simply by using networks containing automatically varying resistors. Figures 6 and 7 are examples of such networks.

In Fig. 6 a potentiometer A is connected across a source of modulation energy. Part of this potentiometer is ordinary resistance but another part is an automatically variable resistance such as Thyrite. Output from the potentiometer is taken wholly or partly from across the Thyrite. In this case the output is distorted in the manner desired. The resistance of the Thyrite decreases automatically with increasing current in a manner to progressively decrease the output for higher instantaneous modulating potentials of either polarity. The amount and variation of distortion can be adjusted by varying the amount of fixed resistance in series or parallel with the Thyrite in input and output portions of the circuit, by varying the dimensions of the Thyrite resistor, and by varying the value of modulation voltage and current impressed upon the network.

Fig. '7 is an elaboration of Fig. 6 showing various variable circuit elements for carrying out adjustrnents needed for obtaining the desired distortion characteristics more exactly.

Transmitters in accordance with my present invention may be received by any of several types of receivers which have been made available. In one type of receiver, for example, the carrier wave, at an intermediate frequency in a superheterodyne system, is taken out through a filter, separately amplified, and then recombined with the whole signal or its side frequencies. The phase of the reintroduced carrier is made controllable and by varying the phase adjustments the receiver may be set for receiving either amplitude modulation or phase modulation of the kind produced by my present invention. Throughout the foregoing specification and in the following claims, the terms connected and coupled used to recite the connections between the various elements of the circuits, have been used interchangeably, both being given equivalent meanings and each being intended to cover conductive, inductive, resistive, or capacitive connections alone or combinations of such connections.

Having thus described my invention and the operation thereof, what I claim is:

1. A signalling device comprising a source of carrier frequency waves, a source of modulating potentials, a phase modulator connected with said source of carrier frequency Waves and with said source of modulating potentials, a pair of thermionic tubes having their control grids connected in pushpull relation to said phase modulator, and their anode circuits connected in pushpull relation with an output circuit, neutralizing devices interconnecting the electrodes in said tubes, a rectifier of the full wave type having its input electrodes coupled to said source of modulating potentials, a pair of thermionic modulator tubes having their control grids connected to the output circuit of said rectifier and their anodes coupled together, a source of direct current potential, and a circuit connecting the anodes of said last named tubes and the anodes of said first named pair of tubes in parallel with said source of direct current potential.

2. Signalling means comprising a phase modulator connected with a source of carrier frequency energy, and with a source of modulating potentials to accomplish phase modulation of the carrier frequency energy in accordance with the modulating potentials, and means for eliminating or reducing any side frequencies or unwanted frequency components appearing in the output of said phase modulator comprising a pair of thermionic tubes having their control grids connected in pushpull relation to said modulator, their anodes coupled to a load circuit and to a source of direct current, a pair of thermionic tubes having their anodes connected to said source of direct current, a rectifier having its input electrodes connected to said source of modulating potentials, and a circuit connecting the output of said rectifier to control electrodes in said last named pair of thermionic tubes.

3. A signalling device comprising a source of carrier frequency waves, a source of modulating potentials, a phase modulator connected with said source of carrier frequency waves and with said source of modulating potentials, a pair of thermionic tubes having their control grids connected in pushpull relation to said phase modu-.

lator, and their anode circuits connected in pushpull relation with an output circuit, a rectifier of the full wave type having its input electrodes coupled to said source of modulating potentials, a pair of thermionic modulator tubes of the screen grid type having their screen grids connected to a resistance in the output circuit of said rectifier and their anodes coupled together, a source of direct current potential, and a circuit connecting the anodes of said last named pair of tubes and the anodes of said first named pair of tubes in parallel with said source of direct current potential.

4. Means for producing a modulated carrier Wave having a frequency spectrum equivalent to an amplitude modulated wave but with the phase of the carrier shifted ninety degrees which includes means for successively phase modulating and amplitude modulating a carrier Wave in accordance with modulating potentials, and means including an automatically variable resistor con-,

nected with said amplitude modulating means in the path of said modulating potentials to modify the form thereof for modifying the amplitude modulation response to the modulating potentials.

5. Means for producing a modulated carrier wave having a frequency spectrum equivalent to an amplitude modulated wave but with the phase of the carrier shifted ninety degrees, including means for successively phase modulating and amplitude modulating a carrier wave in accordance with modulating potentials, and means including a repeating device connected with said first named means for modifying the form of the modulating potentials to thereby modify the amplitude modulation response to the modulating potentials.

6. Means for producing a modulated carrier wave having a frequency spectrum equivalent to an amplitude modulated wave but with the phase of the carrier shifted ninety degrees comprising, a

source of modulating potentials, a phase modulator and an amplitude modulator connected thereto, and means including non-linear repeating devices interposed between said source of modulating potentials and said amplitude rnodulator for modifying the form of the modulating potentials and thereby modifying the modulation response of the amplitude modulator to the modulation energy. Y

'7. In a signalling system, a source of high frequency oscillations, a source of modulating potentials, a full wave rectifier, an amplifier having input and output electrodes, a source of direct current potentials, a phase modulator, a first circuit coupling said phase modulator to said source of high frequency oscillations, a second circuit coupling said phase modulator to said source of modulating potentials, a third circuit coupling said full wave rectifier to said source of modulating potentials, means coupling said amplifier input electrodes to said phase modulator, means coupling the output electrodes of said amplifier to said source of direct current potentials, and current absorbing means of variable impedance coupling said rectifier to said source of direct current potentials.

8. A signalling system as recited in claim '7 wherein non-linear distorting resistances are interposed in said second circuit.

9. A signalling system as recited in claim 7 in which non-linear distorting resistances are interposed in said third circuit.

10. A signalling system as recited in claim 7 wherein non-linear distorting-resistances are interposed in said second and third circuits.

11. The method of decreasing the frequency spectrum of phase modulated waveenergy without decreasing the phase deviations of said wave energy from a mean phase which includes the step of increasing the energy of the phase modulated wave an amount which increases with deviation of the phase of the modulated energy ahead of or-behind the mean phase of the wave energy.

12. The method of decreasing thefrequency spectrum of phase modulated carrier wave energy without decreasingthe phase deviations of said wave energy from a mean phase which includes the steps of, amplifying the phase modulated wave energy, andmodifying the amplitude of the wave energy resulting from amplifying said phase modulated wave energy in accordance with the numerical value (regardless of sign) of the phase deviation of said wave energy from the mean phase thereof.

13. The method of signalling which includes the steps of, modulating the phase of a carrier wave at signal frequency, and changing the amplitude of the modulated wave in the same direc tion in accordance with the absolute value of the phase deviation thereof in either direction relative to said carrier to reduce the energy of undesired side frequencies.

14. The method of signalling which includes the steps of, controlling the phase of a carrier wave at signal frequency, and additionally modulating the amplitude of the components which result from such phase control in accordance with the absolute value of said phase control.

15. The method of signalling by means of carrier frequency oscillations and modulating potentials which includes the steps of, varying the phase of said carrier frequency oscillations in accordance with said modulating potentials, producing impulses the intensity of which are characteristic of the modulating potentials, and increasing the amplitude of the resulting phase modulated energy in accordance with the intensity of said impulses.

16. The method of signalling by means of carrier frequency oscillations and modulating potentials which includes the steps of, distorting said modulating potentials, varying the phase of said carrier frequency oscillations in accordance with said distorted modulating potentials, rectifying the modulating potentials a rd varying the character of the resulting phase modulated energy in accordance with the rectified modulating potentials.

17. The method of signalling by means: of carrier frequency oscillations and modulating potentials which includes the steps of, varying the phase of said carrier frequency oscillations in L accordance with said modulating potentials, producing voltage characteristic of said modulating potentials and harmonically related thereto and increasing the amplitude of the resulting phase modulated energy in accordance with the said characteristic voltage.

18. The method of signalling which includes the steps of, producing carrier waves of constant frequency, producing modulating potentials of signal frequency, shifting the phase of the carrier waves in accordance with the modulating potentials to produce carrier energy and sideband energy of the first order and other undesired components and modulating the amplitude of the total energy in the same direction non-linearly with respect to said modulating potentials to eliminate the undesired components.

19. The method of signalling which includes the steps of, producing carrier waves of constant frequency, producing modulating potentials of signal frequency shifting the phase of the carrier waves in accordance with the modulating potentials to produce carrier energy and sideband energy of the first order and other undesired components, rectifying the modulating potentials: to obtain voltage components characteristic of the modulating potentials and harmonically related thereto, and simultaneously varying the character of the total energy resulting from said phase modulation in accordance with said voltage components.

20. The method of producing a modulated wave comprising a carrier and first order sidebands related as in a phase modulated wave which includes thesteps of, modulating the phase; of a carrier wave in accordance with signal potentials to produce resultant phase modulated energy, producing potentials of an amplitude which varies substantially as the square of the said modulating potentials and increasing the amplitude of the said modulated energy in'accordance with said produced potentials.

21. The method of producing a modulated wave comprising a carrier and first order sidebands related as in a phase modulated wave which includes the steps of, distorting modulating potentials, modulating the phase of a carrier wave in accordance with said distorted modulated potentials to produce resultant phase modulated energy, producing potentials of an amplitude which vary substantially as a square of the modulating potentials and increasing the amplitude of the said modulated energy in accordance with said produced potentials.

22. The method of producing a modulated wave comprising a carrier and the phase of the sidebands related as in a phase modulated wave which includes the steps of modulating the phase of a carrier wave in accordance with signal potentials to produce resultant phase modulated energy, producing potentials of an amplitude which vary substantially as the square of the said modulating potentials and of a frequency double the frequency of the said modulating potentials and increasing the amplitude of said modulated energy in accordance with said produced potentials;

23. In a signalling system a source of carrier Wave oscillations, a source of signalling potentials, a phase modulator having input terminals connected to said source of carrier wave energy, said phase modulator having output terminals, a linear impedance and a non-linear impedance in series connected across said source of modulating potentials, a circuit connecting said resistances with said phase modulator, a pair of relay tubes each having a control grid and a cathode and an anode, a circuit coupling the control grids of said tubes to the output terminals of said phase modulator, a circuit connecting the anodes of said tube to a source of direct current potential, an impedance in said last named circuit, an amplifier having input and output electrodes, a connection between said output electrodes and said impedance, a rectifier having input and output electrodes, a connection between the input electrodes of said rectifier and said source of modulating potentials, a third impedance connected with the output electrodes of said rectifier and fourth impedance connecting the output electrodes of said rectifier to the input electrodes of said amplifier.

24. A system as recited in claim 23 in which said third impedance is of the non-linear type.

25. A system as recited in claim 23 in which said fourth impedance is of the non-linear type.

26. In a signalling system a source of carrier wave energy, a source of modulating potentials, a phase modulator having input terminals coupled to said source of carrier wave energy, said phase modulator having output terminals, a resistance connected in shunt to said source of modulating potentials, a variable resistance connecting an additional non-linear resistance and a third resistance in shunt to a portion of said first named resistance, a circuit connecting said nonlinear resistance and said third resistance to said phase modulator, a pair of relay tubes each having a control grid and an anode, circuits connecting the control grids of said tubes to the output terminals of said modulator, a circuit connecting the anodes of said tubes to a source of direct current potential, an amplifier tube having a control grid and an anode, a circuit connecting the anode of said amplifier tube to said source of direct 0 rent potential, '2. rectifier having an input coupled to said source of modulating potentials, said rectifier having an output, a pair of impedances connected with the output of said rectifier, and a connection between the juncture point of said impedances and control electrode of said amplifier.

27. A system as recited in claim 26 in which one of said impedances is of the non-linear type.

28. Signalling means comprising a phase modulator including means for causing phase deviations in wave energy in accordance with modulation potentials from a source of modulating potential, and means for relaying said modulated wave energy and for eliminating any side frequencies or unwanted frequency components inadvertently caused and appearing in the output of said phase modulator comprising a pair of tubes each having a controlling electrode and an anode and having their controlling electrodes connected in push-pull relation to said phase modulator and their anodes connected to a source of direct current potential and a full wave rectifier having input electrodes connected to said source of modulating potentials for said phase modulator and having output electrodes connected to said source of direct current potential.

29. Signalling means comprising, a phase modulator connected with a source of carrier frequency energy, and with a source of modulating potentials to accomplish phase modulation of the carrier frequency energy in accordance with the modulating potentials, and means for relaying said phase modulated energy and for substan tially eliminating side frequencies or unwanted frequency components appearing in the output of said phase modulator comprising a pair of tubes each having a controlling electrode and an anode and having their controlling electrodes connected in push-pull relation to said modulator, a full wave rectifier having an input and an output, a load circuit, means connecting the anodes of said tubes to said load circuit and to the output of said full wave rectifier, means connecting the input of said full wave rectifier to said source of modulating potentials, and neutralizing devices interconnecting the anodes and controlling electrodes of said tubes.

30. Signalling means comprising a phase modulator connected with a source of carrier frequency energy, a wave distorting circuit connecting said phase modulator with a source of modulating potentials to accomplish phase modulation of the carrier frequency energy in accordance with distorted modulating potentials, and means for reducing side frequencies or unwanted frequency components appearing in the output of said phase modulator comprising a pair of tubes each having a controlling electrode and an anode and having their controlling electrodes connected in push-pull relation to said phase modulator, a load circuit, means coupling the anodes of said tubes to said load circuit, a rectifier having input electrodes and output electrodes, means coupling the anodes, of said tubes to the output electrodes of said rectifier and means coupling the input electrodes of said rectifier to said source of modulating potentials.

31. In a system for producing a modulated carrier wave, having a frequency spectrum. equivalent to an amplitude modulated wave but with the phase of the said carrier wave shifted 90, a source of carrier wave energy, a source of modulating potentials, means connected with both of said sources for phase modulating said carrier Wave energy in accordance with said modulating potential and additional means connected with said last named means and said source of modulating potentials for amplitude modulating the phase modulated carrier to eliminate undesired sideloands of a higher order inadvertently accomplished in said phase modulating means.

32. Apparatus according to claim 31 including additional means connected with said phase modulating means for modifying the wave form of the phase modulation and its effect upon the modulated output energy.

33. Means for producing a modulated carrier Wave, having a frequency spectrum equivalent to an amplitude modulated wave but with the phase of the carrier shifted 90, including means for successively phase: modulating and amplitude modulating a carrier wave in accordance with modulating potentials, and means including automatically variable resistors for distorting the modulating potentials used for phase modulating said carrier tom-.od-ify the phase modulating response to the modulation potentials.

34. Means for producing Wave, having a frequency spectrum equivalent to an amplitude modulated wave but with the phase of the carrier shifted including means for successively phase modulating and amplitude modulating a carrier wave in accordance with modulating potentials, said means for phase modulating said carrier waveyincluding a nonlinear tube device which responds non-linearly to the modulating potential for modifying the phase modulation response to the modulating energy.

a modulated carrier 35. Means forproducing a modulated carrier wave, having a frequency spectrum equivalent to an amplitude modulated wave but with the. phase of the carrier shifted 90 comprising a source of carrier wave energy, a source of modulating potentials, a phase modulator connected to both of said sources, and an. amplitude modulator connected to said phase modulator and said source of modulating potential, and means for controlling the action of said phase modulator including a non-linear repeating device interposed between said source of modulating poten-- tials and said phase modulator.

36. A modulating system comprising a source of modulating potentials, a source of carrier wave energy, and a phase modulator in which some amplitude modulation is inherently produced connected to said source of carrier wave energy and to said source of modulating potential, and. means for modifying the action of said phase modulation, to obtain the desired output therefrom comprising a circuit including a linear resistance in series and a non-linear resistance in parallel with said circuit in said connection between said source of modulating potentials and saidphase modulator.

37. Apparatus according to claim 31 including a means for modifying the wave form of the modulating potentials used for amplitude modulating the phase modulated carrier energy to modify the effect of said modulation upon the modulated output energy.

CLARENCE W. HANSELL. 

